Papers › Exact CMB B-mode power spectrum from anisotropic cosmic birefringence

Exact CMB B-mode power spectrum from anisotropic cosmic birefringence

21 Apr 2024arXiv:2404.13771links table onlyarchive 2025-07-28

Toshiya Namikawa

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We calculate the cosmic microwave background (CMB) B-mode power spectrum resulting from anisotropic cosmic birefringence, without relying on the thin approximation of the last scattering surface. Specifically, we consider the influence of anisotropic cosmic birefringence arising from massless axion-like particles. Comparing our results to those obtained using the thin approximation, we observe a suppression in the amplitude of the B-mode power spectrum by approximately an order of magnitude at large angular scales (ℓ≲10) and by a factor of two at small angular scales (ℓ≳100) when not employing the thin approximation. We also constrain the amplitude of the angular power spectrum of the scale-invariant anisotropic cosmic birefringence using the SPTpol B-mode power spectrum. We find that the amplitude is constrained as A_(CB)×10⁴=1.03^(+0.91)_(-0.97) (2 σ). The numerical code is publicly available at https://github.com/toshiyan/biref-aniso-bb/tree/main.

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